1. Field of the invention
The present invention relates to an image forming apparatus which enables printed output of a visible image on a recording medium by means of developing an electrostatic latent image on an image carrier through use of a development device.
2. Background Art
An image forming apparatus compatible with a color image has recently become widely prevalent. Some pieces of image forming apparatus compatible with a color image have four development devices assigned to respective color components of YMCK, and a rotary (revolving body) unit having the development devices disposed around a rotary shaft of the rotary unit. In the image forming apparatus having such a configuration, the respective development devices integrally rotate in association with rotation of the rotary unit, whereby the development devices sequentially move to a development position where the development device faces a photosensitive drum which serves as an image carrier. Consequently, after having developed an electrostatic latent image on the photosensitive drum as a toner image, the development device located at the development position transfers the toner image to an intermediate transfer body, or the like. These operations are sequentially repeated such that the toner images formed by the respective development devices are superposed one on top of the other on the intermediate transfer body or the like, so that a transfer image corresponding to the color image is formed on the intermediate transfer body or the like.
In the electrophotographic image forming apparatus, the electrostatic latent image on the photosensitive drum is generally developed as a toner image. Accordingly, the concentration of toner, the amount of remaining toner, and the like greatly affect the image quality of a formed image. In view of this, an image forming apparatus, which has a rotary unit and is compatible with a color image, has hitherto been proposed to detect and monitor—through use of a custom-designed sensor, or the like—the concentration of toner, the amount of remaining toner, a determination as to whether or not the development device is attached to a predetermined position within the rotary unit, a determination as to whether or not a toner cartridge, which is a constituent unit of the development device, is attached, and the like, whereby the image quality of the formed image can be maintained favorable. Specifically, proposed configurations are as follows: Namely, a custom-designed sensor, or the like, is disposed at a fixed position proximate to the outer circumferential surface of, e.g., the rotary unit. The state of the development device opposing the fixed position is detected. Further, the development device in the rotary unit is provided with a sensor for detecting the concentration of toner, or the like. Exchange of a signal with the sensor or supply of power is performed by an optical communication unit, to the sensor through use of a current. In view of limitations on securing of motor space or power supply, a drive source, such as a motor disposed outside the rotary unit, imparts driving force—which is used for causing the development devices in the rotary unit to perform development operation—solely to the development device, which has rotationally moved to and come to stop at the development position and remains stationary.
However, an image forming apparatus having a related-art rotary unit subjects the development devices located outside the position, where an electrostatic latent image on the photosensitive drum is developed, to detection of a state of the development device, such as the concentration of toner, the amount of remaining toner, and attachment/detachment of the development device, or detection of a state of a constituent unit of the development device such as attachment/detachment of a toner cartridge, as well as to acquisition of a signal pertaining to a result of detection. Specifically, the development devices located outside the development position are subjected to detection of a state of the development device or detection of a state of a constituent unit of the development device.
The state of a development device that is in the course of developing an electrostatic latent image cannot be detected. Sufficient detection accuracy cannot always be acquired in connection with a physical quantity whose highly-accurate information can be detected by means of detecting the state of the development device in a driven state, such as the concentration of toner.
In some image forming apparatus equipped with a rotary unit, pitches between the development devices on the outer circumference of the rotary unit are nonuniform. When the image forming apparatus is compatible with formation of a monochrome image as well as formation of a color image, the amounts of consumed toner of YMCK color components do not necessarily become uniform. In relation to toner of a color component which is consumed in large amounts, an increase in the volume of the toner cartridge in the developing machine is effective for lessening the frequency of replenishment of toner.
However, when the development devices are arranged at nonuniform pitches, the development position is the only position where all the development devices always stop. Therefore, when state detection is performed at a position other than the development position, a custom-designed sensor, a sensing signal exchange unit, or the like, is arranged at a plurality of locations in order to detect the states of respective development devices. Alternatively, when none of the development devices are located at the development position, there may arise a necessity for stopping the rotary unit. In short, operation required by the development devices arranged at nonuniform pitches may result in complication of the configuration of the image forming apparatus, a drop in productivity relating to image formation, or the like.